The present application relates to semiconductor devices, and more particularly to devices which are capable of switching relatively high voltages, e.g. of 50V or more, while remaining reasonably compatible with integrated circuit fabrication techniques.
Many power devices are designed as vertical devices, where the direction of carrier flow is into the semiconductor material (normal to the surface of the wafer). However, there are many advantages to “lateral” power devices, i.e. to transistors which have their direction of carrier flow approximately parallel to the surface. One outstanding attraction of lateral devices is process compatibility, since lateral devices can usually be fabricated with process steps which are the similar to or at least compatible with those used for low-voltage devices. Another attraction is that lateral devices tend to be somewhat easier to integrate with low-voltage devices, to provide “smart power” or “integrated power” functionality.
However, MOSFET and JFET structures that are manufactured with their channel regions at the top surface of the die have the amount of active channel limited by the surface area of the die. This limits the current-carrying capability available for a given footprint or cost.
High-Voltage Transistor Fabrication with Trench Etching Technique
The present application describes structures and methods for significantly increasing the amount of active channel that can be obtained for a lateral power device in a given area. This is done by using trenches to form sidewall-gated JFETs and/or depletion mode MOSFETs. Although the direction of current flow is lateral, the effective active channel now extends into the die as deeply as the trench etch permits.
The disclosed innovations, in various embodiments, provide one or more of at least the following advantages:                On-resistance can be reduced for a given footprint.        The total current-switching capability for a given footprint can be increased.        The total current-switching capability for a single die can be increased.        The heat dissipation for a given process flow and footprint can be decreased.        By addition of a deep trench etch, an integrated power process can obtain high current-switching capability.        Depletion-mode device fabrication is particularly easy.        